There is a growing interest in natural ingredient beauty products and products that prevent and reduce aging symptoms as well as products that can protect the skin from various environmental stress. A multitude of components from various sources have been used in cosmetic products, although evidence of beneficial effects of individual components is in some cases very limited.
Algae, both macroalgae (“sea weed”) and microalgae, have been used in cosmetic products as thickening agents, water-binding agents, and antioxidants. Certain macroalgae, such as Irish moss and carrageenan, are used as a source of natural proteins, vitamin A, sugar, starch, vitamin B1, and minerals including iron, sodium, phosphorus, magnesium, copper, and calcium. Algae typically found in cosmetics include Ulva lactuca, Ascophyllum, Laminaria longicruris, Laminaria saccharine, Laminaria digitata, Alaria esculenta, various Porphyra species, Chondrus crispus, and Mastocarpus stellatus. Microalgae have as well been used in cosmetic compositions, these include Chlorella, Spirulina, Dunaliella and Odontella species.
U.S. patent application published as U.S. 2005/0123499 A1 discloses a cosmetic composition comprising at least two of the following ingredients: algae extract, sea fennel and Codium Tamentosum extract. A specific example contains a mixture of a Chlorella extract sold under the trade name CHLORELLINE®, an extract obtained from Ulva Lactuca sold as AOSAINE®, and a green flower extract obtained from Monostroma. Other cosmetic products which comprise algae are disclosed in published patent applications FR 2834886A, JP2004051568A2, JP 2005047860A2, FR 2838340A, FR 2838341A, FR 2838342A, FR 2806906A, FR 2850277A, FR2796556A, JP11228437A and JP005415A.
Although the mechanism behind skin aging is not completely understood, the cosmetic market offers an enormous variety of anti-aging products. Most of the products available are directed to the mechanisms of stimulating collagen and glycosaminoglycan synthesis by fibroblasts in the epidermis, lowering free radical levels in the skin or increasing firmness and flexibility of the stratum corneum.
Skin Barrier Enhancement
The skin barrier, also referred to as the epidermal permeability barrier, protects against infection and poisoning, prevents desiccation and is essential for terrestrial life. Barrier function is conferred by the outer layer of epidermis, the stratum corneum which consists of dead, keratin-filled cells embedded in a lipid matrix. Stratum corneum is formed from granular layer keratinocytes during terminal differentiation of normal adult epidermis. A rapid aggregation of the keratin cytoskeleton, which causes a collapse of the granular cells into flattened a nuclear squames, is a key step in formation of the outermost barrier layer of the skin. This condensed cytoskeleton is cross linked by transglutaminases during formation of the cornified cell envelope (CE). Transglutaminases are expressed and activated during terminal differentiation of keratinocytes. The membrane-bound form of the transglutaminase-1 forms ester bonds between specific glutaminyl residues of human involucrin during formation of the cornified cell envelope enzyme. The CE not only prevents water loss but also impedes the entry of allergens and infectious agents. During the last stage of its terminal differentiation of keratinocytes is the formation of a cross linked envelope. This envelope is made up of membrane and cytosolic proteins cross linked by glutamyl lysine isopeptide bonds. Involucrin, being a keratinocyte protein which appears first in the cytoplasm and later becomes cross linked to membrane proteins by transglutaminase, is the most abundant component is of the envelope. Loricrin is another major component of the cross linked cell envelope of the epidermis of the skin, also known as the cornified cell envelope (CE). Filaggrin is a protein which is expressed in granules in the granular layer of interfollicular epidermis which is predominantly composed of the protein pro-filaggrin. Upon terminal differentiation of granular cells, pro-filaggrin is proteolytically cleaved into filaggrin peptides. Filaggrin aggregates the keratin cytoskeleton and is therefore a key protein in facilitating epidermal differentiation and maintaining barrier function.
Agents that enhance and improve the natural skin barrier function as described above are useful in cosmetic products, e.g. for improving retention of moisture in the skin, lessening dry skin formation and for generally keeping the skin in a healthy and visually appealing condition.
Anti-Aging Effect by Induction of Collagen Synthesis
Medical research has demonstrated that a cause of wrinkle formation is induction of MMP-1 expression due to photoaging leading to collagen degradation, which cannot be compensated by a concomitant induction of collagen synthesis (Scharfetter et al., 1991). This imbalance is further increased by the fact that UVA irradiation results in a decreased expression of Collagen 1A1 and Collagen 1A2 (Südel et al., 2005). The transcription factor AP1 is activated upon UVA stimulation and exerts the induction of MMP-1 and the repression of Collagen 1A1 and Collagen 1A2 (Chung et al., 1996). Hence, agents that stimulate collagen synthesis and preferably as well inhibit photo-induced up-regulation of MMPs would be very beneficial in cosmetically active skin-care products to provide an anti-aging effect.
The term “skin aging” relates generally to the thinning and/or general degradation of the dermis. This involves a decrease in collagen gene expression, lower fibroblast activity and fibroblast regeneration as well as shrinking of the lamellar barrier, which is shown in the inability of the skin to retain moisture. Accordingly, the term “anti-aging” as used herein refers to an effect which counteracts skin aging, i.e., acts against the above effects for retaining smooth and healthy skin.
Photoaging and Photo-Protection of Skin
Exposure of human skin to ultraviolet (UV) light induces multiple deleterious effects in the epidermis and dermis. UVB (290-320 nm) radiation primarily causes photo carcinogenesis due to its direct interaction with cellular DNA and subsequent formation of cyclobutane pyrimidine dimers, 6-4 photoproducts and thymine glycols. The major consequence of UVA (320-400 nm) radiation is the generation of reactive oxygen species, which, however, can also induce cancer, e.g. by generation of oxidized DNA base derivatives like 8-hydroxydeoxyguanosine.
Whereas UVB effects are mainly restricted to the epidermis, UVA rays directly effect the dermal compartment and are therefore thought to be the major factor responsible for photoaging of human skin. It has been shown that especially the long wave part of UVA referred to as UVA1 (340-400 nm) accounts for damaging effects in human dermal fibroblasts, through induction of cytokines, matrix metalloproteinases and mitochondrial DNA mutations. Of these, the induction of collagenase (matrix metalloproteinase-1, MMP-1) which degrades collagen type I, the major constituent of the connective tissue, is of particular significance since the extent of collagen I reduction correlates with photo damage in human skin. It has been postulated that the UVA1-induced up-regulation of MMP-1 is regulated by interrelated autocrine loops of interleukin-1 (IL-1) and interleukin-6 (IL-6); UVA1 radiation rapidly induces bioactivity of extracellular IL-1α and IL-1β which then induce IL-6 expression. IL-1 and IL-6 both enhance the biosynthesis of MMP-1, peaking at 24 h. concomitantly; the de novo synthesis of IL-1 is stimulated leading to a further boost of IL-6 and MMP-1 induction. Consequently, induction of MMP-1 is a useful marker for skin aging. UVA-induced up-regulation of the cytokine IL-6 has previously been shown to be a prerequisite of UVA-induced MMP-1 induction. Therefore, agents that reduce the photo-induced up-regulation of MMPs are potentially very useful for photo-protection by reducing and/or slowing down photoaging.